<!DOCTYPE html>
<html>
<head>
<style>
div {
background-color: green;
}
div[mixedCase=true] {
background-color: red ! important;
}
</style>
</head>
<body onload="document.getElementById('d').removeAttribute('mixedcase');">
<div id="d" mixedcase="true">text</div>
</body>
</html>
